Estimation du flux de sève du kiwi par bilan de chaleur en conditions semi-contrôlées : note technique

Dans le bilan d'eau du sol d'une savane (végétation éparse) l'exactitude de l'estimation de la transpiration des ligneux est le facteur déterminant la précision d'estimation de l'évapotranspiration réelle totale de la savane. Pour mesurer la transpiration (flux de sève des ligneux) nous avons utilisé la méthode du bilan de chaleur. Nous faisons un rappel théorique de la méthode, décrivons le dispositif de mesure et présentons quelques résultats concernant des individus de kiwi. Les résultats nous permettent d'affirmer que la méthode du bilan de chaleur donne des résultats satisfaisants. L'absence d'étalonnage, le pas de temps, et la souplesse de mise en place (capteurs "sur mesure") sont d'excellents arguments pour que l'on applique cette méthode à l'étude de l'évapotranspiration réelle des savanes. (Résumé d'auteur

Estimation du flux de sève du kiwi par bilan de chaleur en conditions semi-contrôlées : note technique

Dans le bilan d'eau du sol d'une savane (végétation éparse) l'exactitude de l'estimation de la transpiration des ligneux est le facteur déterminant la précision d'estimation de l'évapotranspiration réelle totale de la savane. Pour mesurer la transpiration (flux de sève des ligneux) nous avons utilisé la méthode du bilan de chaleur. Nous faisons un rappel théorique de la méthode, décrivons le dispositif de mesure et présentons quelques résultats concernant des individus de kiwi. Les résultats nous permettent d'affirmer que la méthode du bilan de chaleur donne des résultats satisfaisants. L'absence d'étalonnage, le pas de temps, et la souplesse de mise en place (capteurs "sur mesure") sont d'excellents arguments pour que l'on applique cette méthode à l'étude de l'évapotranspiration réelle des savanes. (Résumé d'auteur

Performance of GNSS-R GLORI data for biomass estimation over the Landes forest

The Above-Ground Biomass (AGB) is a key parameter used for the modeling of the carbon cycle. The aim of this study is to make an experimental assessment of the sensitivity of Global Navigation Satellite System (GNSS) reflected signals to forest AGB. This is based on the analysis of the data recorded during several GLORI airborne campaigns in June and July 2015, over the Landes Forest (France). Ground truth measurements of tree height, density and diameter at breast height (DBH), as well as AGB, were carried out for 100 maritime pine forest plots of various ages. The GNSS-R data were used to obtain the right-left (Γ RL ) and right-right (Γ RR ) reflectivity observables, which are geo-referenced in accordance with the known positions of relevant GPS satellites and the airborne receiver. The correlations between forest AGB and the GNSS-R observables yield the highest sensitivity at high elevation angles (70°-90°). In this case, for (Γ RL ) and the reflectivity polarization ratio (PR = Γ RL /Γ RR ) estimated with a coherent integration time Tc = 20 ms, the coefficients of determination R 2 are equal to 0.67 and 0.51, with a sensitivity of −0.051 dB/[10 6 g (Mg) ha −1 ], and −0.053 dB/[Mg ha −1 ], respectively. The relationships between AGB and the observables are confirmed through the use of a 5-fold cross validation approach, with several different coherent integration times

The AQUI Soil Moisture Network for Satellite Microwave Remote Sensing Validation in South-Western France

Global soil moisture (SM) products are currently available thanks to microwave remote sensing techniques. Validation of these satellite-based SM products over different vegetation and climate conditions is a crucial step. INRA (National Institute of Agricultural Research) has set up the AQUI SM and soil temperature in situ network (composed of three main sites Bouron, Bilos, and Hermitage), over a flat area of dense pine forests, in South-Western France (the Bordeaux⁻Aquitaine region) to validate the Soil Moisture and Ocean salinity (SMOS) satellite SM products. SMOS was launched in 2009 by the European Space Agency (ESA). The aims of this study are to present the AQUI network and to evaluate the SMOS SM product (in the new SMOS-IC version) along with other microwave SM products such as the active ASCAT (Advanced Scatterometer) and the ESA combined (passive and active) CCI (Climate Change Initiative) SM retrievals. A first comparison, using Pearson correlation, Bias, RMSE (Root Mean Square Error), and Un biased RMSE (ubRMSE) scores, between the 0⁻5 cm AQUI network and ASCAT, CCI, and SMOS SM products was conducted. In general all the three products were able to reproduce the annual cycle of the AQUI in situ observations. CCI and ASCAT had best and similar correlations (R~0.72) over the Bouron and Bilos sites. All had comparable correlations over the Hermitage sites with overall average values of 0.74, 0.68, and 0.69 for CCI, SMOS-IC, and ASCAT, respectively. Considering anomalies, correlation values decreased for all products with best ability to capture day to day variations obtained by ASCAT. CCI (followed by SMOS-IC) had the best ubRMSE values (mostly < 0.04 m3/m3) over most of the stations. Although the region is highly impacted by radio frequency interferences, SMOS-IC followed correctly the in situ SM dynamics. All the three remotely-sensed SM products (except SMOS-IC over some stations) overestimated the AQUI in situ SM observations. These results demonstrate that the AQUI network is likely to be well-suited for satellite microwave remote sensing evaluations/validations

Potential applications of GNSS-R observations over agricultural areas : results from the GLORI airborne campaign

The aim of this study is to analyze the sensitivity of airborne Global Navigation Satellite System Reflectometry (GNSS-R) on soil surface and vegetation cover characteristics in agricultural areas. Airborne polarimetric GNSS-R data were acquired in the context of the GLORI'2015 campaign over two study sites in Southwest France in June and July of 2015. Ground measurements of soil surface parameters (moisture content) and vegetation characteristics (leaf area index (LAI), and vegetation height) were recorded for different types of crops (corn, sunflower, wheat, soybean, vegetable) simultaneously with the airborne GNSS-R measurements. Three GNSS-R observables (apparent reflectivity, the reflected signal-to-noise-ratio (SNR), and the polarimetric ratio (PR)) were found to be well correlated with soil moisture and a major vegetation characteristic (LAI). A tau-omega model was used to explain the dependence of the GNSS-R reflectivity on both the soil moisture and vegetation parameters

The FluxSAP 2010 hydroclimatological experimental campaign over an heterogeneous urban area

International audienc

FluxSAP 2010 experimental campaign over an heterogeneous urban zone, part 1: heat and vapour flux assessment

International audienc

Fluxo de seiva pelo método do balanço de calor: base teórica, qualidade das medidas e aspectos práticos Sap flow by heat balance method: theoretical basis, data quality and practical aspects

O método do balanço de calor representa uma técnica importante para estudos sobre fisiologia vegetal, agrometeorologia e irrigação. Sua aplicação tem aumentado nos últimos anos em decorrência da maior facilidade de importação de material e equipamentos e do uso mais disseminado dos sistemas automáticos de aquisição de dados. Avanços importantes em diversas áreas de pesquisa têm sido alcançados com a possibilidade de se quantificar o consumo hídrico em plantas isoladas em diferentes escalas de tempo. Com base na teoria do método, esta revisão tem como objetivo apresentar e discutir os procedimentos de instalação, manutenção e de análise e processamento dos dados com vistas ao uso mais adequado da técnica e à obtenção de dados mais confiáveis e coerentes. Aspectos relacionados à influência das condições ambientais no funcionamento do sensor são abordados; são também discutidas diversas recomendações práticas observadas na literatura disponível. O grande número e a diversidade de procedimentos que envolvem a instalação dos sensores, sua manutenção em condições de campo e a análise dos dados conferem ao método grande aplicação na experimentação científica. Entretanto, o uso do método de balanço de calor em larga escala parece inadequado devido à dificuldade de correta operação, o que facilmente compromete a qualidade das medidas.<br>The stem heat balance method has become an important technique in plant physiology, agrometeorology and irrigation science. Its application has increased in the last years due to the development of less expensive automatic data acquisition systems that are widespread. Important advances in several research areas have been reached by quantifying the water consumption by isolated plants in different temporal scales. Based on the theory of the method, this review aims to present and discuss the procedures of installation and maintenance, and data analysis and processing, giving elements to improve the user's criticism about data quality. Aspects related to the impact of environmental conditions on sensor performance are presented, as well as the practical recommendations found in literature are critically discussed. The method is a useful tool for research and experimentation, but it seems to be inadequate for use in practical conditions. Difficulties involving its operational and practical aspects - installation and maintenance in field conditions - in addition to data analysis and processing are the main obstacles to the users of this technique